The present invention relates to two low-cost devices for quantitative measurements of gaseous constituents in ambient air. The measurement system integrates diffusive gas sampling technology with spectrophotometric analysis into a single package which can be reused and re-analyzed numerous times. An example of this system is a carbon monoxide occupational dosimeter (LOCD) and indoor air quality (IAQ) passive sampler. This invention is a result of a collaborative effort between Lawrence Berkeley National Laboratories (LBNL) and Quantum Group, Inc., CRADA No. BG94-204(00).
A need exists for a passive sampler for population-based exposure assessment, particularly a dosimeter for the measurement of workplace and residential exposures to carbon monoxide.
An inexpensive occupational dosimeter that is,designed to measure CO exposure during an 8-hour work shift and an inexpensive passive sampler capable of measuring one-week average indoor CO concentrations in residences were developed. The devices use a simple quantitative method to assess time-weighted-average (TWA) workplace or residential exposures to CO. The device provides researchers and industrial hygienists with a means to conduct cost effective surveys of occupational CO exposures and residential indoor air quality studies.
The occupational dosimeter should be capable of measuring time weighted CO concentrations ranging from 10 to 800 parts-per-million-hours (ppm-h), i.e., 8-hour work-shift TWA CO concentrations of 1 to 100 ppm. An accuracy of xc2x120% and a precision of xc2x110 ppm-h at exposures above 40 ppm-h is required. These sampling ranges are appropriate for CO exposure assessment based upon the permissible levels set by regulatory bodies. The current Personal Exposure Limit (PEL) set by the U.S. Occupational Safety and Health Administration (OSHA, 1993) is 50 parts per million measured as a time-weighed-average (TWA) over 8-hours. The National Institute for Occupational Safety and Health (NIOSH) recommends an exposure limit of 35 ppm TWA for 8-hours (NIOSH, 1972), and the American Conference of Governmental Industrial Hygienists recommends a Threshold Limit Value (TLV) of 25 ppm TWA for 8-hours (ACGIH, 1991].
Conceptually, the passive sampler and the occupational dosimeter both operate on the principle of gas diffusion sampling (Rose, 1982; Palmes, 1976). They require no pump. CO reacts on the surface of the sensor so that the surface CO concentration is close to zero. In the LBNL/QGI diffusion sampler design the sensor is encased in a small vessel, with a tube that communicates from the inside, at the sensor surface, to the outside air. A removable plug at the opening of the tube is used to control CO diffusion to the sensor. Since the CO concentration ([CO]) at the sensor surface is zero, a CO partial pressure gradient exists along the tube, from CO laden environmental air to the sensor. When the plug is removed, this partial pressure gradient drives a diffusive flow of CO along the tube to react at the surface of the sensor. As the sensor reacts with CO, it changes color in a manner that can be used to assess CO exposure quantitatively. The sampling period is defined as the period for which the sampler""s plug is removed from the diffusion tube.
A need exists for low-cost methods of quantitative determination of gas-phase constituents of ambient atmospheres. The measurement system described in this document integrates diffusive gas sampling technology with spectrophotometric analysis into a single package which can be reused and re-analyzed. This invention covers both the general sampling and measurement system and the carbon monoxide dosimeter and indoor air quality passive sampler.